The present invention relates to hollow toy parts and, in particular, to soft hollow doll heads. The invention also relates to a method for making soft, hollow toy parts with thermoplastic elastomers, and to the molds used in those methods.
Traditionally, soft, hollow toy parts or doll heads were made by either by slush molding, dip molding, or rotocasting processes using latex or PVC, or by blow-molding processes using thermoplastic elastomers. These traditional processes, however, are not able to make hollow parts with controllable and precise wall thicknesses and opening dimensions. Nonetheless, due to the softness and easy processing of PVC, slush molding and rotocasting processes using PVC have been the primary process and the primary material for making one-piece hollow doll heads with direct hair rooting in the past half century.
In the last decade, however, various research has indicated that PVC material is not environmentally friendly, and more importantly, it may also be harmful to one""s health. As a result, some toy manufacturers have been asked to stop using PVC in toys and dolls. Accordingly, there is a need for new materials that are not harmful and do not cause environmental concerns for use in making toys. As well, there is a need for a new process for making soft hollow toy parts with controllable and precise wall thicknesses and opening dimensions.
The present invention provides a solution to the aforementioned needs. In one aspect of the invention, a method is provided for making a soft hollow part for a toy, such as a head for a doll. The method includes providing an injection moldable flexible thermoplastic elastomer, and providing a mold for the head part. The mold includes exterior mold parts and an interior core part, wherein the exterior mold parts are spaced apart from the interior core to define a cavity in the shape of the hollow part to be formed. The thermoplastic elastomer is injected into the mold cavity to form the hollow head. The head has an opening for removing the interior core, but the dimension of the core is larger than the dimension of the opening through which the core must be removed. After the head is injection molded, the exterior mold parts are opened to release the head and interior core, and then the interior core is removed from the head by extracting it through the opening in the head.
Preferably, this method uses a non-PVC thermoplastic elastomer. In particular, a family of flexible thermoplastic elastomers known as S-B-S (Styrene-Butadiene-Styrene), S-I-S (Styrene-Isoprene-Styrene) and S-EB-S (Styrene-Ethylene/Butylene-Styrene), marketed by Shell Chemical Company under the name KRATON, is preferred because of its resilience, strength and durability, as well as the ability to be painted and passing the general paint adhesion requirements for toys and dolls applications. S-B-S copolymer, such as marketed as KRATON D, is the more preferred elastomer. This copolymer is reported to be environmentally friendly, and not harmful to people""s health.
In a second aspect of the invention, a mold is provided for making an injection molded hollow article, such as a doll head, using a thermoplastic elastomer. The mold includes an exterior mold portion and an interior core assembly. The exterior mold portion includes at least separable two sections for enclosing the interior core assembly. The interior core assembly fits inside the exterior mold portion. The interior core is spaced apart from the exterior mold portion to define a variable-thickness cavity having the shape of the hollow article to be molded and into which a melted thermoplastic elastomer may be injected to form the hollow article. The hollow article takes the shape of the cavity and includes an opening through which the interior core is removable. The interior core assembly has a cross-sectional dimension that is larger than the dimension of the opening in the hollow article from which it must be removed after the article is molded. Accordingly, this mold is useful for making a variety of hollow toy parts that have a narrow opening, such as heads, feet, hands, etc.
In a third aspect of the invention, an injection-molded hollow doll head is provided. The hollow doll head is made of an injection-moldable thermoplastic elastomer. The doll head has an exterior surface defined by an opposing surface of an exterior mold, and an interior surface defined by an opposing surface of an interior mold core during the injection molding process that formed the head. The interior surface of the hollow head defines a hollow interior of the head that is in communication with an opening at the bottom of the head. The hollow interior has a major hollow dimension larger than the dimension of the opening.
In one embodiment, the doll head preferably includes a pull-tab projecting from the top of the head. When the head is injection molded, a part line is created at the junction of two exterior mold halves. The part line extends along the lateral edges of the pull-tab, across the ears and down the sides of the he ad to the opening.
In another embodiment, the doll head is made without an observable part line. When the head is injection molded, a part line is created at the junction of two exterior mold halves. The part line extends in a continuous line around the top of the head above the ears. Hair-material is rooted to the top of the doll head above and below the part line with a sufficient density such that the part line is not observable to an ordinary observer holding the doll at arms length.
Preferably, the invention takes advantage of certain mold structures to make the soft hollow parts and dolls heads. A multi-piece removable and splitable solid interior core assembly may be used to mold soft hollow parts with a major hollow dimension significantly larger than the removal opening dimension, as shown in FIGS. 1-4. A one-piece solid core may be used to mold soft hollow parts or doll heads with a major hollow dimension larger than the removal opening, as shown in FIG. 5. A two-part solid core design with a mushroom-shaped ejector pin, double-ejection system may be used to locate the parting line at the top part of head within the hair rooting area, as shown in FIGS. 6-8, to make the part line not observable to the ordinary observer. A pull tab may be molded on the doll head to assist with removal of the head from the interior core, as shown in FIG. 8.
The process of this invention allows a toy manufacturer to make soft hollow toy parts and doll heads using thermoplastic elastomers with several advantages over the traditional processes. First, controllable and precise wall thicknesses can be achieved at specific locations. Second, by the use of multi-piece interior cores, there is no virtual limit on the undercut ratio of the hollow interior to the core removal opening. Third, all kinds of injection moldable thermoplastic elastomers can be used, especially, environmentally friendly and non-harmful materials.
These and other features and advantages of the invention will be apparent and fully understood from the following Detailed Description of the Preferred Embodiments of the Invention, taken in connection with the appended drawings.